1. Field of the Invention
The present invention relates generally to semiconductor integrated circuit processing, and more specifically to an improved method for forming a diffusion barrier layers for sub-micron connects in integrated circuits.
2. Description of the Prior Art
In silicon integrated circuit technology, an aluminum alloy is most commonly used for the ultra large scale integrated (ULSI) metallization. However, as device dimensions approach the deep submicron regime, several problems arise. Higher speed and higher electromigration reliability are required, and consequently a new metallization material is needed which offers lower resistivity for reduced RC delay and greater resistance to electromigration. Copper could be used in place of aluminum to answer this need.
However, there are several unresolved issues regarding copper metallization. Cu diffuses rapidly in Si and SiO.sub.2. In an Si substrate, a deep level that acts as a generation-recombination center is formed as a result of diffusion. This causes degradation of junction leakage characteristics.
In order to overcome these problems, researchers have begun to focus upon using what is often called "diffusion barriers". A diffusion barrier is defined as part of the metallization scheme, and comprises a layer of material interposed between an overlying conductor such as copper (Cu) and an underlying contact region such as doped silicon (Si) or silicon dioxide. The overall structure is therefore a multilayer structure. The role of a diffusion barrier is to prevent or at least retard interdiffusion of material on opposite sides of the barrier into one another.
An amorphous alloys with high crystallization temperature and with no grain boundaries are appealing candidates for diffusion barriers because they lack grain boundaries that can act as diffusion paths. For example, amorphous binary silicides, such as (Mo, Ta or W)--Si, and amorphous ternary alloys, such as (Mo, Ta, W or Ti)--Si--N have been disclosed as amorphous diffusion barriers. These amorphous ternary metallic alloys have shown superior barrier properties partly due to their lack of fast diffusion paths.
However, formation of these amorphous ternary alloys involves sophisticated sputtering processes using a transition metal alloy targets with quite uniform composition. Further, sputter deposited ternary alloys introduces large quantities of contaminants during the sputter operation.
Generally speaking, sputter-deposited ternary diffusion barrier produces a brittle thin film with poor adhesion to the sputtering system components. A large number of particles are thereby generated during the sputter process using alloy targets which results in a significant increase in deleterious particulate matter deposited upon the wafer.
Thus, what is needed is to develop a simple and easy process together with minimizing problems relevant to the diffusion barrier.